Over the past 500 million years our planet has borne witness to five mass extinctions of life. We are now bearing witness to a sixth. Unlike previous mass extinctions—which all occurred before the rise of our species—the sixth mass extinction is—at least in part—being driven by man. While cataclysmic natural events—some sudden, others incremental—were the principle causes of prehistoric massive extinctions, the current mass extinction has root causes that are both directly and indirectly attributable to man’s impact on the natural world. The sixth mass extinction is as insidious as it is calamitous.
Mass Extinction – Historical Context
We humans have occupied only a very thin slice of time on this planet. It has been estimated that if the entire history of earth were compressed into a single 24-hour day our species would occupy only about three seconds on that 24-hour clock. 99.9998% of what has transpired on earth happened prior to our existence. A lot happened over the eons of time that we were not privy to—including five historical mass extinctions. A synopsis of those previous extinction events….
Previous Mass Extinctions-The Most Well Known and Understood
Occurring somewhere between 430 and 450 million years ago, the Ordovican-Silurian Event ranks as the second worst extinction event in our planet’s history. Evidence indicates that ~85% of marine life went extinct during this period. No definitive cause(s) have been identified but several potential contributors have been hypothesized. Those theories would include gamma ray bursts, extreme volcanic activity, glaciation (causing catastrophic drops in global sea-levels), and metal poisoning.
Earth’s most disastrous extinction occurred ~250 million years ago. The Permian-Triassic Extinction is also know as the “Great Dying”, and for good reason. By the end of that event the earth had lost ~ 70% it its land-based vertebrate species and an unimaginable 96% of its marine life. This event also wreaked havoc on insects, wiping out ~60% of all insect families.
Unlike the Ordovican-Silurian Event, in which the diversity of life recovered relatively quickly, it took ~10 million years for the earth to regain even a semblance of its previous bio-diversity.
Causes of this extinction event have been narrowed down to just a few likely culprits: massive asteroid impact, increased volcanic activity, and anoxia.
Occurring ~200 million years ago, the Triassic-Jurassic Extinction set the stage for the subsequent domination of the dinosaur during the Jurassic period. This event eliminated ~50% of all existing species and resulted in an environment in which dinosaurs had little or no competition. The event, from start to finish, was only 10,000 years in duration. A mere blip in geologic time when compared to some of the other extinction events.
Although there is no hard consensus as to cause of this extinction the list of potential culprits would include the usual offenders . Super volcanoes and asteroid impact are at the top of most lists. The asteroid theory has the most adherents even though no suitable remnant crater has been located.
Alas, our beloved Tyrannosaurus Rex met his ignominious end ~ 66 million years ago. T-Rex and all of his dinosaur compatriots were flashed out of existence during the Cretaceous-Paleogene Extinction Event. The extinction was so complete that no quadruped weighing more than 60 pounds survived. In this case, the small and meek did indeed inherit the earth. It was the dawn of the rise of mammals.
Most experts agree that this extinction event—the 5th— was caused by the aftermath of an asteroid impact. Such an impact would have had destructive power equivalent to several million nuclear weapons. A very bad day indeed!
We can be thankful that our species was only a proverbial glint within some benevolent eye during all of the above events. We can also truthfully state that we are blameless. That was the case then. That is not the case now…..
The Sixth Mass Extinction
We are now witnessing a sixth mass extinction. The Holocene Extinction Event —corresponding to the Holocene epoch in which we are now living—has mankind as its principle root cause. This ongoing extinction has impacted a wide range of plants and animals. Entire habitats have been devastated.
All previous mass extinctions events encompassed tens or hundreds of thousands of years. The Holocene event is no different. The onset of the current event dates back ~ 20,000 years, roughly corresponding to the onset of mankind’s ascendancy. Over those millennia our species has successfully cultivated and domesticated much of our environment. We have also devastated it. That devastation continues. Much of our activity has been noble in nature, some of it….no so much. But, whether noble or gluttonous, in many cases the results have been the same. The ways in which we have instigated/aggravated the current extinction event would include—but not be limited to—the following:
- Human population growth. We have simply crowded out many other living organisms.
- Massive agriculture. Moving from hunter-gathering to farming was good for us but hard on many ecosystems.
- Habitat and population destruction. We have deforested, over-fished, and over-hunted.
- Pollution: To varying degrees we have polluted air, water, and soil.
We humans have been designated as a “Global Super-Predator”. Very hard to come up with an objective argument against that moniker. We have taken much and repaid little.
Global Impact of the Sixth Mass Extinction
In his book The Future of Life, E.O.Wilson put forth a calculation predicting that, if unchecked, the current rate of human disruption of the biosphere will result in the extinction of 50% of existing higher lifeforms by the year 2100. A staggering prognosis. Some studies have shown that many animal species have lost 70 to 80% of their populations since 1900. Even those among us that typically scoff at such pessimism should at least pause and reflect upon such potential outcomes.
Whether optimist, pessimist, or realist there is no escape from truth and reality. We are losing species at an alarming rate. Adding to this dire situation is the fact that many species go extinct without us even being aware of their demise. They were here on the very edges of our awareness and they vanish with no fanfare. However, there are many well-known cases of extinction or near-extinction. A very small fraction of those would include…..
An Unfinished Course
The Sixth Mass Extinction is nowhere close to running its course. The only question is what the final tally will be and whether or not we can do anything to help mitigate that tally. Increased awareness of what is happening around us seems a logical first step. Beyond that, only time and the quality of our efforts will tell.